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Future Climate/Environmental Change (Next 100 years) (Problems and…
Future Climate/Environmental Change (Next 100 years)
Class
Types of Prediction
1. Intuitive
Uses the basic physics that if GHG concentrations increase, then global temperatures will rise
Along with an appreciation of the climatic system, this leads to the following predictions:
I)
The temperature rise will be most obvious at high latitudes and altitudes because of the dramatic visible effects on the cryosphere
II)
Land areas will warm more rapidly than the oceans
III)
Night-time temperatures are likely to increase more than day-time temperatures.
IV)
Higher temperatures will increase atmospheric water vapour, so there will be more intense precipitation events and stronger storms.
V)
Atmospheric circulation patterns could change so that some areas become wetter while others become dryer and more drought-prone.
VI)
Shifting climate belts will result in environmental change and adverse impacts on the biosphere.
VII)
Sea-levels will rise but at differential rates
All these patterns are important, but are too vague for specific policy-making decisions
2. Paleo-Environmental Reconstructions
I.e. using the past as a guide to what we can expect in the future
Reconstructions of past conditions reveal that GHG levels and climate have fluctuated dramatically over the last 900,000 years
-
Low GHG
concentrations have corresponded to
colder
climates (Glacial episodes / Glaciations) and low sea-levels, while
warm periods
have been characterised by
high GHG values
and high sea-levels
Reconstructions of past ‘glacials’ and ‘inter-glacials’ show that each has been
slightly different
, the following information can be added to intuition-based predictions:
Polar Amplification will occur, i.e. the temperature changes will be greatest at higher latitudes
There have been warmer interglacials than the present one - SL in the previous interglacial, for example, was 5 metres higher than it is today
There are a number of changes that characterise the transition from glacial to interglacial conditions (but it's important to note that these changes may not be set in stone as human's influences may dominate in future):
Decrease in polar realm extent
Increase in tropical realm extent
Decrease in the extent of arid areas (due to increased availability of atmospheric water vapour)
Increase in global terrestrial biomass
Sudden, dramatic changes in climate, often at the regional scale, are evident from records - mostly due to sudden, huge releases of cold melt-water into the oceans (but highly unlikely to occur in the coming century as the formative conditions are not right)
Rapid rates of SL rise are also evidenced in the record, but again, this is unlikely to happen for us in the next 100 years as:
No huge melt-water lakes available to discharge
Greenland is not prone to ice-surges
Antarctica has experienced limited warming to date (however, the risk of the ice-shelf collapse cannot be entirely dismissed)
Overall, these records, combined with intuition-based predictions, can go as far as providing a conceptual framework but insufficient detail regarding amounts, rates of change and timings needed for sensible decision making
3. The 'Extrapolation' Approach
I.e. using the immediate past as a guide to the future
Relies on uniformitarianism reasoning
Extrapolation is problematic due to:
It's ability to only cover a limited period of time, over which something like contemporary conditions of GW have prevailed - i.e. from the late 1970s onwards, thereby currently limiting predictions to 30years
The ‘post-2000 pause’ and the regional variation in rates of temperature rise (see Fig.F8), essentially make such an approach invalid, as they assume linearity in terms of response, i.e. the rate of climate change will not vary over time
They assume that the geographic pattern of past change will be replicated in the future, i.e. ‘stationarity’, but as they have clearly changed in the past the approach is invalid
They are greatly affected by natural climatic variability
Extrapolation, based on dangerous assumptions of linearity and stationarity, is therefore wholly unsuitable as a basis for planning
4. Mathematical Models
(i.e. the only reliable way)
Possibly the greatest challenge for science has been creating these models: scale, complexity, lack of existing knowledge and urgency must all be overcome
Evolved from weather forecasting models developed in the 1960s
They apply a series of fundamental equations that determine atmospheric motion to a three-dimensional grid of data points using powerful computers
In order to simulate climate change, the range and complexity of the inputs have had to increase dramatically, necessitating ever larger computers and longer run-times
Limitations that had to be overcome
:
Required a
3-Dimensional grid of data-points
No such grid of primary data existed, so it had to be generated based on the records provided by “hospitable”/ inhabited areas.
This frequently meant extrapolation over time and space.
The relatively recent availability of satellite measurements has helped considerably, but there are still problems (e.g. soil moisture)
Needed to make models of atmospheric motion in order to produce Atmospheric General Circulation Models (AGCMs)
These
cannot predict future climate without including information about the oceans
and the
interrelationship
between atmosphere and oceans (‘ocean-atmosphere coupling’).This clearly meant that:
Information had to be collected about the oceans
Ocean General Circulation Models had to be developed: Originally 'slab oceans' i.e. only dealt with the shallow surface layer w/o currents, but subsequently, extended to include surface currents, deeper flows and oscillations such as ENSO (Hansen, 1981, showed the improved accuracy resulting from including the thermocline with the mixed layer)
Putting the OGCM and the AGCMs were expensive and time consuming
Additional information had to be supplied and modelled, such as ‘Biospheric Contributions’ and the effects of changing sea-ice distribution
Each of the 30 models used in the IPCC 2007 report had to be validated against the known pattern of change since pre-industrial times (1860)
The basic tools used are GCMs (General Circulation Models) which represent physical processes in the glo- bal atmosphere, oceans, ice sheets and on the land’s surface:
Resolution: Generally 1-3 degrees in latitude and longitude; to give perspective; everything between Manchester and the South Coast of Britain would be accumulated together - much too coarse to give usable guidance
Issue 1: Zooming in and repeating model equations: bears the risk of blowing up any inher- ent weakness of the ‘mother’ model. If the model does a poor job of simulating certain atmospheric patterns, those errors will be com- pounded at the regional level
Issue 2: In regions with complex topography, such as where mountains form a wall between two climatically different plains, models can be very poor
Simulations remain an important tool for understand- ing processes, such as changes in river flow, that global models just cannot resolve
2 Main Types of Prediction
Approach 1: Predictions as to the
types and scales
of change/adverse impact that are likely to occur across regions /continents
arising from a set level of temperature rise
Easier to produce, because they indicate what will happen
‘if’
certain levels of warming occur
but not ‘when’
they will be achieved
More of a multiple scenario-based approach
E.g. Stern's 'Projected Impacts of Climate Change' which shows the effects on food, water, ecosystems, extreme weather and major, irreversible changes as the global temperature increases from its current value
Approach 2: Calculate the
spatial distribution of change in conditions over time
, so that change at specific locations can be assessed at different times in the future
More useful for policy makers but harder to achieve
E.g. IPCC predictions
From
approach 2
there are
4 main types of such predictions
:
All except mathematic models are inadequate
What does the IPCC do?
Looks at what a doubling of CO2 from pre-IR levels will do
This is called 'climate sensitivity'
They've given a range of possible values:
Low: +1.5C
Best Estimate: +2.5C
High: +4.5C
Sensitivity is split into 2 components:
Primary: Achieved by the gas
Secondary: Further temperature rise due to the operation of geosystem processes
Came up with 4 different emissions scenarios:
A1 Family: Very rapid economic growth, rapid introduction of new and more efficient technologies and population stabilisation by mid-2100s and then decline
A2 Family: A more heterogeneous world with spatial variations in population growth, rate of economic development and technological innovation
B1 Family: Similar to A1 but with less resource use and greater emphasis on Global solutions to economic, social and environmental problems highlighting sustainability
B2 Family: Describes a patchwork of local patterns of population growth, economic development and environmental sustainability. Global population continues to rise, but less than in A2, while economic growth and technological innovation are less than in the A1 and B1 scenarios
I.e. B1 is the best scenario, and A2 is probably the worst
NOTE: IPCC 2013-2014:
The above have now been replaced with new scenarios focused on the possible range of radiative forcing values by 2100AD compared with pre-industrial levels
These are known as ‘Representative Concentration Pathways’ or RCPs
They give similar, but more realistic, assessments than the previously employed ‘Emission Scenarios’ (Houghton, 2015)
The Predictions
Main Features:
Warming increases with latitude, especially in the N. Hemisphere (Smithson et al., 2008)
Land areas warm more rapidly than oceans (Houghton, 2009's global map shows the temperature rise by 2090 compared to 1980)
Night-time temperatures will rise more rapidly than day-time temperatures (i.e. diurnal variation will tend to diminish)
Precipitation changes will be variable and are subject to significant disagreement (Houghton, 2009 shows that the majority of the areas of the global still have less than 66% agreement on future scenario)
The greatest increases will be at high latitudes and mid-latitudes
Increased precipitation over the Northern Atlantic could diminish the strength of the North Atlantic Deep Water (NADW) circulation and thereby reduce the warming effect over NW Europe
Certain areas could become dryer including parts of S. America, much of Africa, parts of Australia, much of the Mediterranean basin and central america and the West Indies
Also likely to be spatially variable changes in rainfall intensity (World Bank, 2010), proneness to droughts (World Bank, 2010 shows places e.g. the Med, California, West Australia, Namibia to be at risk) and amounts of run-off
These predictions should be considered highly uncertain due to the difficulty of predicting the effects of small-scale/local factors
What can then be estimated using these identified patterns of change?
Ecology (Fig. F21).
Sea-level change (see Fig. F.22 and Lectures 35-36).
Agriculture.
Climatic hazards (e.g. extreme weather, hurricanes, etc.) and climate-induced hazards (e.g. floods)
N.B. A recent IPCC report (IPCC 2012) has confirmed the likely increase in extreme weather but has stated that although Tropical Revolving Storms (Hurricanes, Typhoons, Cyclones) may become more powerful, they are unlikely to become more frequent or increase in spatial range.
Water resources,
Health, etc., etc.
Problems and Uncertainties
Issue 1
: The levels of scientific knowledge regarding various aspects of climate change
still remain far from perfect
, i.e.
uncertainty still exists
.
There are two main types of Uncertainty:
Aleatory
(uncertainty or randomness where the outcome is inherently unpredictable)
Epistemic
(uncertainty due to lack of information or knowledge - for example, IPCC 2007's Global annual mean radiative forcings have significant uncertainty, especially cloud albedo effect and aerosol's effect in general)
Issue 2
: whether or not there will be a
smooth continuation
of GW or whether there will be sudden,
unexpected shifts in climate change
due to the crossing of ‘tipping points'
Due to a system reaching “a critical threshold at which the future state of a system can be altered by a small change in forcing” (
Lenton, T. M. et al 2008
)
Passing such thresholds can result in alterations to rates of change of global temperatures/GHGs and the operation of environmental systems such as the atmosphere and oceans
Lenton and Leverman (2012) identify a number of these tipping points:
At around 1.5C, the Yedoma Permafrost will all thaw out at once --> emission of CO2 and big alteration in GW
‘Tipping points’ are still a theoretical concept as no such event has yet been experienced. As a consequence, no such event has yet been built into the models
Issue 3: Rethinking climate sensitivity
: The actual pattern of GW with increasing CO2 led scientists (IPCC 2007) to rethink climatic sensitivity, reducing the likely range to 2.5° – 4.5°C (most likely c3°C)
The “post-2000 plateau” of global temperature rise, has led some to argue that the “best estimate” should be re-evaluated downwards again towards 2.5°C, and even to 2°C, which will have a profound influence on predictions as to the likely magnitude of future temperature rises.
However, as yet there has been no overall support for such a downgrading and 2.5⁰C remains the accepted value
Issue 4
: Attempts to calibrate models with respect to climate change over longer periods of the past (i.e. the past 1000 or so years) are faced with the uncertainty as to what was the actual global pattern of change over this time and the causes -
can't predict the future w/o understanding the past
Issue 5: There remains a lack of knowledge about the future role of water vapour
:
A warmer atmosphere will naturally be capable of holding more water vapour and evapotranspiration rates could increase, but will absolute humidity rates increase and where will this change be most apparent?
CO2 increase --> warming --> increased WV --> 1. Increased Greenhouse Effect + 2. Increase Cloud Cover --> Cloud Cover increases albedo which is likely to decrease warming but the greenhouse effect --> warming --> question of which will dominate
Issue 6
: Effect in terms of the changing spatial distribution of
cloudiness and cloud types
Low
clouds (e.g. cumulus) are dense masses of predominantly water droplets and tend to have a net cooling effect
High
clouds (e.g. cirrus), on the other hand, are thin ice-crystal clouds that have an uncertain effect. Traditionally, they were thought to have a net warming effect because they appeared to trap more out-going radiation than they reflected (relatively low albedo), until recent work suggested that they too actually have a cooling influence (
Loeb and Wong, 2007
), although this has subsequently been contradicted
There's a growing body of evidence to suggest that clouds in general may actually have a warming influence
Issue 7: Regional-scale changes
are essential for planning purposes, but difficult to interpret because of differences between the different models. This is especially true of rainfall predictions
Issue 8
: The production of regional predictions remains limited because of
lack of data and computing power
.
Conclusion
Predictions must not be interpreted as precise/accurate, but rather as estimations involving various levels of uncertainty (as the IPCC do in their 2013/14 paper)
Somewhat surprisingly, the levels of uncertainty are increasing with increasing computational sophistication, and it has to be recognised that accurate predictions for periods of up to 100 years are unlikely to be produced in the near future This is because of TWO distinct groups of problems (see to left)
Although it is important to know what is happening/ could happen at a global scale, such overall changes have to be
re-interpreted in terms of potentially adverse changes at the regional, national and local levels
where local factors come into play (as we know from SL lectures)
Clearly important because decision-making is actually driven/ undertaken at a national or local scale, and yet the details are less clear
unless further data inputs are obtained
for the new,
denser
grid that is required
1. Uncertainty and Attribution
Difficulty in terms of distinguishing “natural” influences from ‘anthropogenic’ influences and apportioning changing strength to each over time - even more difficult when doing this for the future
2. Uncertainty and the Temporal Horizon
For <25 years into the future, there's
randomness
due to climatic variability
For 25-50 years into the future, there's a
lack of knowledge
due to scientific uncertainty
For more than 50 years into the future there's a
range of possibilities
due to human actions/scenarios
Introduction
Change in SL and change in climate are the two big concerns for future GW issues
Global Warming:
Increased energy receipt from the sun
Reduction in the amount of incoming energy reflected back to space
Increased volume of atmospheric gases that absorb both incoming and outgoing radiation (i.e. the Greenhouse Effect)
Tyndall (1860): observed that gasses such as
CO2, ozone and water vapour
absorb the Earth’s infrared radiation and heat up more rapidly than the rest of the atmosphere
Arrhenius (1895) calculated that increasing atmospheric CO2 would cause climate change (warming) and that a
doubling of CO2 could increase global temperature by 5°-6C
Callendar
(1938) calculated that the burning of fossil fuels could lead to a temperature rise of 2°C
Greenhouse Gases
Water Vapour is the most prominent but often excluded from discussions due to uncertainty in how humans are modifying WV concentrations
CO2 is then the most prominent:
Pre-IR: 280ppm
2015: 400ppm
Rising by around 2.5ppmpa
CH4 (Methane), N2O (Nitrous Oxide), CFCs (Chlorofluorocarbons) raise the 400ppm to between 435-485ppm of CO2e (CO2 equivalents)
Note that there is a large disagreement about how to translate to CO2e
The Low Dome ice core in Antarctica shows a clear indicator of the massive increase in CO2 concentrations since the IR
Similarly, Mauna Loa in Hawaii shows a steadily increasing trend in CO2 (1955-2015 - note that in the winter, CO2 levels rise due to the lack of vegetation sequestering CO2
Anthropogenic Emissions (2004)
56.6%: CO2 from fossil fuels
17.3%: CO2 from deforestation and biomass decay
14.3%: CH4 Emissions
Note: Each molecule has 25x the warming potential of CO2
7.9%: N2O emissions
Note: Each molecule has 298x the warming potential of CO2
2.8%: Other CO2 sources
1.1%: F-Gases
Houghton, 2015
has documented these changes and noted that the average rate of emissions has increased post-2000
Change and Variability
The UNFCCC 1992 recommended that 'Climate Change' be restricted to changed caused by human activity and that everything else should be lumped under 'Climate Variability'
This approach isn't recommended due to the way human and natural processes combine in complex ways and are both modified by processes operating within the Geosystem
Instead, we should focus on disaggregating the human influences from the overall effect
Expected Future Changes
Climate warming
Continued shrinkage of the Cryosphere
Sea-Level rise
Changing precipitation patterns
Increased extreme weather
Ecosystem disruption
Species extinction (at an increased rate)
it is important to note that adverse consequences are due to the combined effects of global ‘systemic’ and local ‘cumulative’ effects, with the latter often being the most important
Spread of Disease
E.g. Malaria and Dengue Fever: as the average temperatures rise, higher-altitude, colder places will become warm enough to allow mosquitos to survive
Severe water shortage
Changes in rainfall regime and increasing demand, especially where annual water flows have been controlled by mountain glaciers and snowfields
Changing patterns of agricultural activity (involuntary)
Collapse of certain socio-economic systems (theorised, not proven)
Huge numbers of environmental refugees
Political unrest and potential wars as a result of the above (a contested point)
Denial/Scepticism:
ICM (2009) Report on UK population:
7% of people deny CC
39% believe GW is not proven to be human-caused
BBC (2010) Poll:
Only 26% accepted Human-Induced CC was occurring
Reasons for Denial and Scepticism:
The rise in temperatures has been seen to be 'faltering'
Claims that detrimental impacts of CC don't seem to be that bad (e.g. current SL rise)
Claims that any changes are due to natural factors
Urban-dwellers are increasingly decoupled from nature and thus are less exposed/aware of the changes
Main impacts are in areas that are little used by humans (e.g. polar latitudes)
General feeling that trace gases surely couldn't be responsible for such as huge impact
3 Unexpected Events for Scientists:
The post-2000 pause was completely unpredicted
The reduction in volume of some mountain glaciers and shrinkage of summer sea-ice has been unexpectedly great
The collapse of the Antarctic ‘Larsen A’ and ‘Larsen B’ ice-shelves in 1995 (4200km2) and 2002 caused concern until it was found to be due to specific local conditions - but now there is evidence that many West Antarctic ice-shelves are showing signs of stress, raising fears that they may soon be threatened with collapse
Problems for Policy Makers
Mitigation (reducing the scale of future CC)
Adaptation (reducing adversary consequences through adjustment)
Both require anticipatory action as the response of climate systems to changing GHG inputs is slow
Even the existing GHG load alone will cause 0.3C more warming in the future
Past Questions
Explain why climate modellers are cautious about producing precise predictions of climate change over the short-term (<25 years), medium term (25-50 years) and even the long term (50-100 years) - 2014
Predicting future Global Climate Change is fraught with difficulties. Discuss. - 2013
Current predictions of climate change to AD2100 appear compelling but actually suffer from a number of areas of uncertainty. Discuss. - 2012
Predictions of global change by AD2100 are clearly of value, but decision makers require estimations at the regional and local levels and these are much more difficult to produce. Expand on this statement with respect to either climate change OR sea level change. - 2011